How to Use PHP's mysqli_num_rows to Get the Row Count of a Result Set

When performing database operations with PHP, you often need to know how many rows a query returned; the mysqli_num_rows function makes this straightforward.

Below is a complete example that demonstrates connecting to a MySQL server, executing a SELECT query, and using mysqli_num_rows to obtain the row count:

<?php
// Assume a successful connection to the database
$mysqli = new mysqli('localhost', 'username', 'password', 'database_name');

// Check connection
if ($mysqli->connect_errno) {
    echo "连接数据库失败：" . $mysqli->connect_error;
    exit();
}

// Execute query
$query = "SELECT * FROM users";
$result = $mysqli->query($query);

// Verify query success
if (!$result) {
    echo "查询失败：" . $mysqli->error;
    exit();
}

// Get number of rows in the result set
$num_rows = mysqli_num_rows($result);

// Output the count
echo "结果集中的行数为：" . $num_rows;

// Close the connection
$mysqli->close();
?>

The script first establishes a connection, runs a SELECT statement, stores the result in $result, then calls mysqli_num_rows($result) to retrieve the count, storing it in $num_rows and finally echoing the value.

Note that mysqli_num_rows should only be called after a successful query; if the query fails, the result set is empty and the function will return 0.

Using mysqli_num_rows is a practical way to determine whether data was returned and to count rows in PHP‑based backend applications.